An inkjet printing system typically includes one or more printheads and their corresponding ink supplies. Each printhead includes an ink inlet that is connected to its ink supply and an array of drop ejectors, each ejector consisting of an ink pressurization chamber, an ejecting actuator and a nozzle through which droplets of ink are ejected. The ejecting actuator may be one of various types, including a heater that vaporizes some of the ink in the pressurization chamber in order to propel a droplet out of the orifice, or a piezoelectric device which changes the wall geometry of the chamber in order to generate a pressure wave that ejects a droplet. The droplets are typically directed toward paper or other recording medium in order to produce an image according to image data that is converted into electronic firing pulses for the drop ejectors as the recording medium is moved relative to the printhead.
A common type of printer architecture is the carriage printer, where the printhead nozzle array is somewhat smaller than the extent of the region of interest for printing on the recording medium and the printhead is mounted on a carriage. In a carriage printer, the recording medium is advanced a given distance along a media advance direction and then stopped. While the recording medium is stopped, the printhead is moved by the carriage in a carriage scan direction that is substantially perpendicular to the media advance direction as the drops are ejected from the nozzles. After the printhead has printed a swath of the image while traversing the recording medium, the recording medium is advanced, the carriage direction of motion is reversed, and the image is formed swath by swath.
In an inkjet printer, the face of the printhead die containing the nozzle array(s) is typically positioned near the recording medium in order to provide improved print quality. Close positioning of the nozzle face of the printhead die to the recording medium keeps the printed dots close to their intended locations, even for angularly misdirected jets.
In order to provide the capability of printing across the entire width of the recording medium, and also to allow space for the carriage to decelerate and stop before changing directions to print the next swath, typically the carriage moves the printhead beyond the side edges of the recording medium. Generally the position of the recording medium relative to the printhead die face is fairly well controlled. However, occasionally a sheet of recording medium can have a dog-eared edge. Also occasionally multiple sheets of recording medium can be inadvertently fed at the same time, sometimes resulting in paper jamming and folding in accordion fashion. In such situations, the close proximity of the printhead die face to the nominal position of the recording medium can result in recording medium striking the face of the die as the carriage moves the printhead past the edge of the recording medium. For die faces made of material that is fragile or brittle, such strikes can cause catastrophic damage to the printhead, requiring its replacement. Commonly assigned U.S. Pat. No. 7,862,147 discloses providing inclined surfaces near the printhead die to protect the nozzle face from damaging impact by recording medium. Several patents including U.S. Pat. Nos. 7,018,503, 6,902,260, 5,751,324, and 4,500,895 disclose mounting the printhead die within a recess in the mounting substrate. Such a recess at the mounting substrate can help protect the die, but can add manufacturing complexities.
Inkjet ink includes a variety of volatile and nonvolatile components including pigments or dyes, humectants, image durability enhancers, and carriers or solvents. A key consideration in ink formulation and ink delivery is the ability to produce high quality images on the print medium. Image quality can be degraded if evaporation of volatile components in the vicinity of the nozzle causes the viscosity to increase too much. The maintenance station of the printer typically includes a cap that surrounds the printhead die nozzle face during periods of nonprinting in order to inhibit evaporation of the volatile components of the ink, and also to provide protection against accumulation of particulates on the nozzle face. The capping surface that the maintenance station cap seats against is conventionally provided on the face of the printhead. Such a capping surface on the printhead face is exposed at an opening in the printhead holding receptacle of the carriage. This can present multiple discontinuous interfaces along the carriage scan direction, including the carriage edges at the opening, the capping surface on the printhead face, the inclined surfaces (as in U.S. Pat. No. 7,862,147) and the printhead die. Such discontinuous interfaces can collect ink residue and can catch an edge of the recording medium.
What is needed is a printhead carriage that provides a substantially smooth surface of the portion of the printhead carriage assembly that is close to the recording medium along the carriage scan direction, provides protection for the printhead die, and provides a capping surface and seal for the maintenance station cap to inhibit evaporation of volatile ink components.